Contact metamorphism of siliceous dolomite and impure limestones from the Werfen formation in the eastern Monzoni contact aureole

摘要

The intrusive complex of Monzoni in the western central Dolomites (northern Italy) comprises a suite of pyroxenites, monzogabbros and monzodiorites with solidus temperatures in excess of 1000 deg C which intruded previously unmetamorphosed Permotriassic sediments at less than 5 km depth. At the eastern intrusive contact an approximately 860 m wide contact aureole is developed in the carbonate country rocks. The prograde sequence of mineral parageneses in a siliceous dolomite of the Cencenighe member and in marly limestones of the Val Badia and Cencenighe members of the Lower Triassic Werfen formation indicate peak metamorphic temperatures in excess of 698 deg C at 185 m from the intrusive contact and an outward temperature decrease of approximately 65 deg C per 100 m. The high temperatures in the inner aureole caused formation of periclase from the prograde breakdown of dolomite and formation of melilite and esseneite-rich clinopyroxene.